Various types of compact, lightweight pumps including diaphragms as oscillators have been proposed. In such lightweight pumps, the diaphragms are composed of metallic sheets and piezoelectric elements such as lead zirconate titanate (PZT) adhering to the metallic sheets. FIG. 6 is a cross-sectional view of a pump utilizing a diaphragm as an oscillator (see Japanese Unexamined Patent Application Publication No. 2000-265964, in particular, FIG. 1). A sheet piezoelectric element 101 such as PZT is disposed on the upper side of a hollow box-type casing 100 in a pump A so as to partition the interior of the casing 100. A space 102 is disposed above the piezoelectric element 101 and a pump chamber 103 is disposed below the piezoelectric element 101. Supplying power to the piezoelectric element 101 causes the piezoelectric element 101 to vibrate in its thickness direction, thereby changing the volume of the pump chamber 103.
An inlet orifice 105 is disposed on the right bottom side of the casing 100 and an outlet orifice 106 is disposed on the left bottom side of the casing 100. An inlet path 107 extends to the center area of the casing 100 so as to communicate with the inlet orifice 105, whereas an outlet path 108 extends to the center area of the casing 100 so as to communicate with the outlet orifice 106. A partition wall 110 is disposed in the center area of the casing 100 to separate the inlet path 107 from the outlet path 108. An inlet passage 111 connecting the pump chamber 103 to the inlet path 107 and an outlet passage 112 connecting the pump chamber 103 to the outlet path 108 are disposed in the vicinity of the partition wall 110. A check valve 113 is disposed at the inlet passage 111 and a check valve 115 is disposed at the outlet passage 112. When a driving circuit (not shown) applies a voltage to the piezoelectric element 101, the piezoelectric element 101 vibrates.
In the pump A for circulating a fluid, vibration of the piezoelectric element 101, acting as a diaphragm, changes the volume of the pump chamber 103 such that a fluid is sucked into the pump chamber 103 from the inlet orifice 105 through the check valve 113 and the fluid is discharged from the outlet orifice 106 through the check valve 115. Foam 117 for preventing pump pulsation is disposed in the recessed portions of the inlet path 107 and the outlet path 108 close to the bottom of the casing 100 shown in FIG. 6.
A fluid is circulated by way of pumping, using the minute reciprocating movement of the piezoelectric element 101, so that the size and weight of the pump A are considerably reduced as compared to regular fluid pumps utilizing screws or pistons. However, application of this type of pump in electronic devices such as notebook personal computers or mobile information devices is limited without further miniaturization of the devices.
If a reduction of the entire thickness of the pump A is attempted, the upper section of the casing 100 above the piezoelectric element 101 can be made thinner but the bottom section of the casing 100 cannot be made thinner. The foam 117, the inlet orifice 105, the outlet orifice 106, the inlet path 107, and the outlet path 108 are disposed above the recessed portions and thus miniaturization of the pump is limited due to the height of these components. In fact, the entire thickness of the pump includes the thicknesses of the piezoelectric element 101, the casing accommodating the piezoelectric element 101, the pump chamber 103, the check valve 113 or the check valve 115, and the inlet orifice 105 or the outlet orifice 106, and thus it is difficult to further reduce the entire thickness of the pump. Since mobile information devices such as notebook personal computers are being further miniaturized, the thickness of a pump used in a cooling device for such mobile information devices needs to be further reduced. However, the known pump shown in FIG. 6 is not small enough for application in such devices.